Tunable Optical Frequency Comb with a Crystalline Whispering Gallery Mode Resonator

TLDR

The comb’s frequency spacing equals an integer multiple of the resonator’s free spectral range. The study demonstrates a tunable monolithic optical frequency comb generator. The comb is generated via four‑wave mixing in a crystalline CaF₂ whispering‑gallery‑mode resonator, with the mode spacing tuned by adjusting the pump laser frequency. The device produces a diverse set of optical combs and high‑frequency hyperparametric oscillations, and it can generate tunable narrow‑band microwave signals.

Abstract

We report on the experimental demonstration of a tunable monolithic optical frequency comb generator. The device is based on four-wave mixing in a crystalline calcium fluoride whispering gallery mode resonator. The frequency spacing of the comb is given by an integer number of the free spectral range of the resonator. We select the desired number by tuning the frequency of the pumping laser with respect to the corresponding resonator mode. We also observe a rich variety of optical combs and high-frequency hyperparametric oscillation, depending on the experimental conditions. A potential application of the comb for generating tunable narrow band frequency microwave signals is demonstrated.